How to transform text to multiselect?

I have a text field which I would need to transform into multiselect. Delimiter is comma.
Here is example:

Currently only viable option for me is to do it manually. Or am I missing something that would solve my problem?

Is this transformation something that you need to done just once, or occasionally, or does it need to happen automatically whenever the source data changes?

Would you be updating an existing multiselect field (adding to its existing options), or overwriting it, or creating a new multiselect field?